Intention
When coming up with the concepts for these icons, I tried to stay as close to the original and Tychus icons as possible, while still making them look unique.
If you don't agree with the color choices I have made, feel free to modify the icons on your own.
Implementation
Simply unpack the zip-folder and import the icons into the editor. The default lvl 1,2 and 3 upgrades will be replaced automatically (if the files have been placed under assets/textures within the import window). In order to create the level 4 and 5 upgrades, you will simply have to look up the lvl 3 upgrades under "upgrades" within the "data" tab, copy one of them twice and change the icons under "(Basic) Upgrade: Effects".
Finally, find the corresponding research ability (e.g. "Evolution Chamber - Research" for zerg ground upgrades) and add your new upgrade tier under "(Basic) Ability: Info".
Keep in mind that it is also here where you define the button that represents the upgrade within the command card of the research structure - this is important if you don't want to use the icons featuring a plus.
Please note that this project is work in progress. Everything is subject to change.